In my U.S. Pat. No. 4,398,994, the disclosure of which is incorporated herein by reference, I have described a continuous method of forming decorative patterns of aluminized plastic film and the use of such patterned film in packaging. As is described therein, a web of aluminized polymer film is printed with a pattern of etchant-resistant material, corresponding to the pattern desired on the aluminized surface. Aqueous sodium hydroxide solution having a concentration of up to about 25 wt. % is applied, at a temperature of about 15.degree. to about 100.degree. C., across the whole width of the web to contact the pattern on the web. The sodium hydroxide solution is allowed to remain in contact with the web as it is conveyed for about 0.1 to about 10 seconds to permit the sodium hydroxide to dissolve aluminum only from areas of the web not having the pattern of etchant-resistant material applied thereto. The spent sodium hydroxide solution is washed from the web to leave the pattern of etchant-resistant material on the transparent polymeric film. The various steps of the operation are effected consecutively at a web speed of up to about 1000 ft/min.
The apparatus illustrated in the aforementioned patent utilizes rollers dipping into baths of liquid to effect the various steps. This manner of application of etchant and of wash water has been found to be somewhat inefficient in ensuring a consistent product at high speeds of operation and also to be uneconomical with respect to utilization of sodium hydroxide etchant.
In an attempt to overcome those difficulties, in my U.S. Pat. No. 4,552,614, the disclosure of which is incorporated herein by reference, I have described a procedure in which the etchant is spray applied to the film to impinge thereon, scrapers may be used to assist in removal of etched material, warm water sprays wash the spent etchant from the film surface, the washed film is hot air dried and the air-dried film is chilled-roll cooled. By proceeding in this manner, high speed operations may be effected to produce a consistent product with economical use of etchant.
In addition, in my copending U.S. patent application Ser. No. 723,909 filed Apr. 16, 1985 (now U.S. Pat. No. 4,610,755), the disclosure of which is incorporated herein by reference, I have described a procedure in which the metallized surface of an inert substrate film is printed with a pattern of a water-based printing varnish having an etchant dissolved therein, the pattern is permitted to remain in contact with the metallized surface for a period of time sufficient to etch the pattern onto the metallized surface, spent etchant is washed from the film and the washed film is dried.
In each of my prior procedures, etchant is applied to the metallized substrate surface, the desired pattern is allowed to form, and spent etchant is washed from the etched surface. In order to perform such procedures rapidly on continuous webs of metallized film, as is necessary for economic operation, etchant solutions of elevated temperature and high concentration are required and a washing step is necessary to remove spent etchant.